By: Kendra Quicke

The epidemic of Ebola hemorrhagic fever that began in the West African country of Guinea in March of this year and subsequently spread to the neighboring countries of Liberia and Sierra Leone is caused by an ebola virus, specifically Zaire ebola virus.All ebola viruses belong to the virus family Filoviridae, “filo” meaning “thread” due to the characteristic thread-like form of the virus.Until this most recent epidemic, outbreaks of Ebola have been sporadic and largely confined to Central and Western Africa.According to the World Health Organization (WHO), the 2014 epidemic is the largest in history, tallying more cases and deaths than all previous outbreaks combined. Though the natural animal host, known as the reservoir, for ebola virus is uncertain, evidence indicates that the virus is introduced into human populations through contact with the blood or bodily fluids of an infected animal.Once the virus spills over into humans, it spreads in a similar manner, through direct contact with blood and other bodily fluids (including urine, feces, vomit, saliva, sweat) of an infected person, or objects such as bedding contaminated with any of these.Luckily, ebola virus is not spread via air or water, so catching it on an airplane is unlikely. The virus enters the body through mucous membranes, such as the eyes and mouth, and breaks in the skin. It then infects individual cells by binding to host proteins on the cell surface.The interaction between viral and host cell proteins allow ebola virus to be engulfed by the cell.Once inside the cell, the virus releases its genetic material (RNA) and hijacks the host cell’s RNA replication and protein synthesis machinery in order to produce more viruses identical to itself.The newly-made viruses destroy the host cell and are released to infect more cells.

The ebola virus

In the case of ebola virus, the host cells it infects are the cells of the immune system that are normally involved in fighting off viral infections.The virus either kills the cells outright, or causes them to send the wrong signals to other immune cells, resulting in a depressed and inappropriate immune response that can actually be more harmful to the body than helpful.The fact that ebola virus directly attacks the very cells that are supposed to protect the body is largely what makes it so deadly. Once infected, a person can take anywhere from 2 to 21 days to start showing symptoms, though the average incubation period appears to be 8-10 days.Only once a person is symptomatic can they spread the virus to others.Initial symptoms of Ebola Virus Disease (EVD; previously called Ebola Hemorrhagic Fever), include fever, fatigue, headache and muscle aches.As the disease progresses, patients start exhibiting more severe symptoms, such as vomiting, diarrhea and rash.Eventually, the virus begins to damage the walls of small blood vessels, causing spontaneous bruising and hemorrhage that can lead to organ malfunction.The mortality rate of ebola virus varies depending on the specific strain of ebola virus.The Zaire ebola virus responsible for the current epidemic has a mortality rate of close to 60%.

Unfortunately, there are no FDA-approved vaccines or antiviral therapies for ebola virus to prevent or combat EVD.However, several experimental vaccines and treatments are currently being tested for safety.Additionally, the WHO has deemed it ethical, in certain situations, to administer experimental antiviral treatments to patients suffering from EVD due to the extreme nature of this epidemic.Without a vaccine or other antiviral therapy, treatment for EVD patients is limited to administration of intravenous fluids to combat dehydration and to replace electrolytes that are rapidly lost once blood vessels begin to leak. However, while the severity of the epidemic in West Africa is appreciable and tragic, it is also important to note that there are many other diseases such as influenza, bacterial pneumonia, HIV, malaria and tuberculosis that carry a much greater impact on the human population that we continue to deal with every day. A succinct, illustrated explanation of the dynamics of ebola virus infection and perspective on the overall impact of Zaire ebola virus can be found at this link: http://www.youtube.com/watch?v=sRv19gkZ4E0.

Kendra Quicke is a graduate student in the Microbiology and Molecular Genetics Ph.D. program at Emory University. She is working in a research laboratory studying the immune responses to West Nile virus infection.